The spin coating process is divided into several stages according to the rotation speed of the substrate and the change of the gel. It is divided into several stages: dispensing glue, accelerating the rotating glue, rotating the glue evenly and removing the edges. The third stage of the uniform rotation stage is the thickness of the gel coating. And an important stage of uniformity control.

Epoxy

Before the glue is dispensed, the gel is subjected to sub-micron filtration treatment, otherwise the film may form a comet map, a star map, or generate bubbles. The dispensing phase is the process of depositing a colloidal solvent on the center of the substrate. It can be added by hand or dropped by an equipped automatic dispenser. In general, the automatic dispensing method is automatic mechanized operation, and the thickness, uniformity, and repeatability of the final film are good, and the volatile toxic gas can be reduced without physical contact. Manual dispensing is a manual operation, which is suitable for experimental research and requires high film preparation. The epoxy dispensing process can be either static dispensing or dynamic dispensing. The static dispensing is to deposit the glue in the center of the substrate before the substrate is rotated, and the dynamic dispensing is to rotate the substrate at a certain speed. (usually 500RPM), while dispensing glue. If the gum or substrate is hydrophobic, the dynamic dispensing method can be selected, and the amount of dispensing required for the dynamic dispensing method can be slightly less.

2. Spreading glue - speeding up the rotation

Some solvents in the gel are highly volatile. If the substrate does not accelerate to a set speed in a short period of time, the solvent in the gel will evaporate rapidly, which will cause the viscosity of the gel to increase rapidly, thus affecting Control of coating thickness. During the accelerated rotation phase, the substrate rotates at a certain acceleration, and the colloidal solvent begins to diffuse toward the edge of the substrate, and some of the gelatin begins to be pulled out of the substrate. At the initial stage of acceleration, the colloid is deposited on the substrate at a certain height. On the surface, the bottom of the gel adheres to the surface of the substrate and rotates together. The upper layer of the gelatinous material cannot rotate at the same speed as the substrate due to the inertia, so the gelatinous material forms a spiral shape. As the colloid continues to diffuse toward the edge of the substrate under centrifugal force, the spiral gradually disappears, the colloid becomes thinner and coats the surface of the substrate, and the rotational speed of the coated substrate is completely synchronized. During the accelerated rotation phase of the substrate, high-precision control of the rotational speed and accurate setting of the rotational time are very important. In fact, no matter what kind of properties the gel has, the homogenizer needs to have a high-precision, stable motor rotation speed control system, so that a film with uniform thickness control can be produced.

3. Spin coating

In the constant rotation phase, the viscous force and volatilization of the gel are important factors affecting the thickness non-uniformity of the film. The colloidal solvent has formed a coating of a certain thickness when it is accelerated to a set speed. During the subsequent uniform rotation, since the viscous force of the colloid is still less than the centrifugal force received, the coating continues to diffuse toward the edge of the substrate, and the colloid at the edge of the substrate is continuously drawn, and the thickness of the coating is gradually reduced. At the same time, since the coating has covered the entire surface of the substrate, the evaporation rate of the solvent is accelerated by the rapid flow of air above the substrate, and the viscous force of the colloid is also increased, and a gel which is difficult to flow is formed. At this point, the forces in all directions received by the gel coat are balanced and the thickness of the coating is also final. Finally, at the edge of the coated film, the surface tension of the gel, the glue at the edge portion of the film is difficult to be pulled out of the substrate, forming a thin layer with uneven thickness, and even expanding to the back of the substrate, thus The edge of the slice needs to be processed. The chemical edge removal process including the front and back sides of the substrate and the optical edge removal treatment on the front side of the substrate are removed.

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